public abstract class SocketChannel extends AbstractSelectableChannel
    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, NetworkChannel
    
public abstract class AbstractSelectableChannel extends SelectableChannel


SocketChannel 连接到TCP网络套接字的通道

打开一个SocketChannel并连接到某台服务器
ServerSocketChannel 接受一个新连接 ，创建一个SocketChannel


SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress("http://codefun007.xyz", 80));

socketChannel.close();


ByteBuffer buf = ByteBuffer.allocate(128);
int bytesRead = socketChannel.read(buf);
-1，表示已经读到了流的末尾（连接关闭了）


String str = "hello java nio";

ByteBuffer buf = ByteBuffer.allocate(128);
buf.clear();
buf.put(str.getBytes());
//切换为读模式
buf.flip();
while(buf.hasRemaining()) {
    channel.write(buf);
}

write()方法无法保证能写多少字节到SocketChannel
循环 调用write 直到全部写入

非阻塞模式，connect 方法可能在连接建立之前就返回

socketChannel.configureBlocking(false);
socketChannel.connect(new InetSocketAddress("http://codefun007.xyz", 80));

while(! socketChannel.finishConnect() ){
    // wait 
}


非阻塞模式 ， 将一或多个SocketChannel 注册到 Selector
询问 Selector ， 哪些通道已经准备好读写了